Department of Chemistry, University of Alabama at Birmingham, Birmingham, Alabama 35294, United States.
Biochemistry. 2011 Jan 11;50(1):93-105. doi: 10.1021/bi101288y. Epub 2010 Dec 8.
Retinoid X receptors (RXRs) are ligand-dependent nuclear receptors, which are activated by the potent agonist 9-cis-retinoic acid (9cRA). 9cRA binds to the ligand binding domain (LBD) of RXRs and recruits coactivator proteins for gene transcription. Using isothermal titration calorimetry, the binding of a 13-mer coactivator peptide, GRIP-1, to the hRXRα-LBD homodimer complex containing 9cRA (hRXRα-LBD:9cRA:GRIP-1) is reported between 20 and 37 °C. ΔG is temperature independent (-8.5 kcal/mol), and GRIP-1 binding is driven by ΔH (-9.2 kcal/mol) at 25 °C. ΔC(p) is large and negative (-401 cal mol(-1) K(-1)). The crystal structure of hRXRα-LBD:9cRA:GRIP-1 is reported at 2.05 Å. When the structures of hRXRα-LBD:9cRA:GRIP-1 and hRXRα-LBD:9cRA ( 1FBY ) homodimers are compared, E453 and E456 on helix 12 bury and form ionic interactions with GRIP-1. R302 on helix 4 realigns to form new salt bridges to both E453 and E456. F277 (helix 3), F437 (helix 11), and F450 (helix 12) move toward the hydrophobic interior. The changes in the near-UV spectrum at 260 nm of the hRXRα-LBD:9cRA:GRIP-1 support this structural change. Helix 11 tilts toward helix 12 by ≈1 Å, modifying the ring conformation of 9cRA. Hydrogen-deuterium exchange mass spectroscopy indicates GRIP-1 binding to hRXRα-LBD:9cRA significantly decreases the exchange rates for peptides containing helices 3 (F277), 4 (R302), 11 (F437), and 12 (E453, E456). The structural changes and loss of dynamics of the GRIP-1-bound structure are used to interpret the energetics of coactivator peptide binding to the agonist-bound hRXRα-LBD.
视黄酸 X 受体 (RXRs) 是配体依赖性核受体，可被强效激动剂 9-顺式视黄酸 (9cRA) 激活。9cRA 与 RXRs 的配体结合域 (LBD) 结合，并募集共激活蛋白进行基因转录。本文使用等温滴定量热法，报道了在 20 至 37°C 之间，13 个氨基酸的共激活肽 GRIP-1 与含有 9cRA 的 hRXRα-LBD 同源二聚体复合物 (hRXRα-LBD:9cRA:GRIP-1) 的结合。ΔG 在温度上是独立的 (-8.5 kcal/mol)，并且在 25°C 时，GRIP-1 的结合由 ΔH (-9.2 kcal/mol) 驱动。ΔC(p) 较大且为负 (-401 cal mol(-1) K(-1))。报道了 hRXRα-LBD:9cRA:GRIP-1 的 2.05 Å 晶体结构。当 hRXRα-LBD:9cRA:GRIP-1 和 hRXRα-LBD:9cRA (1FBY) 同源二聚体的结构进行比较时，螺旋 12 上的 E453 和 E456 与 GRIP-1 结合并形成离子相互作用。螺旋 4 上的 R302 重新排列以与 E453 和 E456 形成新的盐桥。F277(螺旋 3)、F437(螺旋 11)和 F450(螺旋 12)向疏水性内部移动。hRXRα-LBD:9cRA:GRIP-1 的近紫外光谱在 260nm 处的变化支持这种结构变化。螺旋 11 向螺旋 12 倾斜约 1 Å，改变了 9cRA 的环构象。氘氢交换质谱分析表明，GRIP-1 与 hRXRα-LBD:9cRA 的结合显著降低了包含螺旋 3(F277)、4(R302)、11(F437)和 12(E453、E456)的肽的交换率。GRIP-1 结合结构的结构变化和动力学丧失用于解释共激活肽与激动剂结合的 hRXRα-LBD 的结合能。
